Dyeing from organic solvents by the exhaust process is regarded as particularly significant, because the process involves chemically simple systems of great economic importance.
In view of the increasing importance of synthetic fibers, particularly polyester fibers, and the possibility of dyeing with homogeneous organic liquors without the addition of water, a great deal of attention has been concentrated on the dyeing of polyester with disperse dyes from organic solvents. Most of the effort appears to be directed toward the development of dyes which can be applied to polyester from organic solvents having a much lower heat of vaporization than water so that the solvent can be recovered by distillation at an acceptable cost. Almost all of the work is being done with nonpolar solvents, such as perchloroethylene. However, thus far only a few disperse dyestuffs have been found which provide a useful color yield when dyed on polyester from perchloroethylene.
Furthermore, polyester (e.g., "Dacron" 54) is not dyeable with cationic dyestuffs in the form of their conventional water-soluble salts unless the fiber is further modified by the introduction of anionic dyesites, e.g., by copolymerization with bis(2-hydroxyethyl)-5-sulfoisophthalate as described in U.S. Pat. No. 3,018,272. It has also been generally recognized that conventional water-soluble cationic dyes tend to be too insoluble in nonpolar solvents, such as perchloroethylene, to have any practical solvent dyeing utility on polyester fibers. For example, the affinity of such cationic dyestuffs for acid-modified polyester when applied from an organic solvent is very low and only very pale shades can be obtained.
It has recently been shown in U.S. Pat. No. 3,660,008 that both unmodified and acid-modified polyester can be dyed with aqueous dispersions of cationic dyes containing counterions derived from strong organic acids, such as electronegatively substituted arylsulfonic acids, by a conventional Thermosol process. However, attempts to dye unmodified polyester by an aqueous exhaust process with these same cationic dye arylsulfonates produces only pastel shades, apparently because of the dissociation and excessive solubility of the dye complex in the aqueous dyebath.
U.S. Pat. No. 3,765,835 discloses the aqueous exhaust dyeing of acid-modified poly(ethylene terephthalate) with aqueous dispersions of cationic dye-arylsulfonate salts.
German OLS 2,010,093 discloses a process for dyeing unmodified polyester in a halogenated organic solvent with cationic dyes in the presence of a solubilizing agent and a dyeing accelerator (i.e., a carrier). In an example, polyester fibers are dyed with a basic blue dye by an exhaust process, the dyebath containing sodium thiocyanate, ethanol and perchloroethylene.
U.S. Pat. No. 3,771,956 discloses a low temperature (90.degree. C) dyeing process for acrylic fibers which employs a dyebath containing a chlorinated hydrocarbon, a basic dyestuff, a nonionic surfactant and water.
U.S. Pat. No. 3,718,428 discloses dyestuff compositions for acrylic fibers containing a preformed water-soluble complex of a cationic dye with a linear C.sub.8-24 alkylarylsulfonic acid, a lower alcoholic solvent, and alkalizing agent and water.
British Pat. No. 1,333,949 discloses a process for dyeing poly(ethylene terephthalate) with a solution or dispersion of a water-insoluble anthraquinone disperse dyestuff in a halogenated hydrocarbon in the presence of 0.2% to 5% of water based on the volume of the halogenated hydrocarbon at a temperature above the boiling point of the azeotrope of the halogenated hydrocarbon and the water, and at a pressure above atmospheric pressure.
British Pat. No. 1,241,143 discloses stable, concentrated basic dye solutions for anionic modified aromatic polyesters containing the basic dyes as their free bases or as salts of monobasic organic acids having from 4 to 30 carbon atoms and additionally a chlorinated hydrocarbon solvent and a monobasic organic acid of from 4 to 30 carbon atoms. Monobasic organic acids having utility in the reference dye solutions include both aliphatic and aromatic acids, which can contain either a carboxylic or sulfonic acid group.
British Pat. No. 1,234,727 discloses an exhaustion process for dyeing anionic group-containing synthetic fibers with basic dyestuffs in a chlorohydrocarbon solution which contains the basic dyestuff in the form of the chlorohydrocarbon soluble base or chlorohydrocarbon soluble salt or adduct of the dye base, and contains at least one amine, amide and/or amine oxide having at least 12 carbon atoms and from 0.1 to 4% by weight of water based on the weight of the chlorohydrocarbon.
British Pat. No. 1,192,984 discloses an exhaustion process for dyeing natural or synthetic fibers including polyester fibers from a dyebath containing an organic liquid immiscible with water, a surface-active dispersing agent and, dispersed in the organic liquid, an aqueous solution or dispersion of a dyestuff insoluble in or at most sparingly soluble in the organic liquid, the water content of the dyebath being not more than 10% by weight and preferably 0.5 to 3% by weight.
K. Gebert, Journal of the Society of Dyers and Colorists, Vol. 87, 509-13 (1971), entitled "The Dyeing of Polyester Textile Fabric in Perchloroethylene by the Exhaust Method", discusses the exhaust dyeing of polyester materials in perchloroethylene with conventional nonionic disperse dyes.